The present invention relates to an electrophotographic-process control apparatus for performing surface electric potential control of a photosensitive body used in an electrophotographic image forming apparatus such as a duplicator and printer. Such an electrophotographic image forming apparatus employs an electrophotographic process in the formation of an output image.
Some kinds of photosensitive bodies such as a selenium based photosensitive body or organic photosensitive body are often used in such electrophotographic image forming apparatuses. In such an electrophotographic image forming apparatus, an electrostatic latent image is formed on the photosensitive body by electrifying and exposing thereof. The formed electrostatic latent image is subsequently developed using developer by the developing system provided in the apparatus. In such an image forming process according to the related art, the following steps are currently used. An electrostatic-latent-image electric-potential comprising a difference between an electrified portion electric-potential and an exposed portion electric-potential is controlled so as to make it constant. Toner concentration in the developing system is controlled under the condition where the electrostatic-latent-image electrical-potential is constant. As a result, the density associated with the output image can be stabilized.
FIG. 2 shows an example of an electrophotographic image forming apparatus in the related art wherein an electrostatic-latent-image electric-potential is controlled so as to be constant.
In FIG. 2, a photosensitive drum body 1 is driven so as to be rotated by means of a driving unit and uniformly electrified by means of an electrifier 2. Then part of the surface of the photosensitive drum body 1 is exposed using a laser so as to form a pattern of an electrostatic latent image on the surface of the photosensitive drum body 1. The formed pattern of an electrostatic latent image is used as a reference for measuring electrified-portion electric-potential and exposed-portion electric-potential appearing on the surface of the photosensitive drum body 1. The electric-potential to be measured is measured by means of a surface-electric-potential sensor 4.
A control-input determination unit 5 varies an electrifying-grid-voltage control-input and an exposure-laser-voltage control-input. This variation is made so as to reduce a difference between measured electrified-portion electric-potential and a corresponding target electrified-portion electric-potential. This variation is made so as to also reduce the difference between the measured exposed-portion electric-potential and corresponding target exposed-portion electric-potential. The respective variation in the electrifying-grid-voltage control-input and exposure-laser-voltage control-input results in respective variation in grid voltage in the electrifier 2 and the laser voltage in an exposure device 3. The respective variation in grid voltage in the electrifier 2 and laser voltage in an exposure device 3 results in respective variation in the electrified-portion electric-potential and exposed-portion electric-potential on the surface of the photosensitive drum body 1.
Such an operation is performed repeatedly until the difference between the respective measured values of electric-potential and exposed-portion electric-potential and the respective target values thereof becomes within a predetermined allowable range.
FIG. 3 illustrates an example of an internal construction of the control-input determination unit 5.
A convergence determination unit 6 calculates the difference between the respective measured values of electric-potential and exposed-portion electric-potential and the respective target values thereof. The convergence determination unit 6 subsequently determines whether or not the difference becomes within a predetermined allowable range. The control-input determination unit 6 consequently obtains a necessary variation amount to which the relevant current control-input is added if the difference is outside of the predetermined allowable range. The result of the addition is used as the relevant subsequent control input of the electrified-portion electric-potential and exposed-portion electric-potential. The above-mentioned obtaining of the necessary variation amount is carried out by multiplying the difference with a control coefficient.
A number 2 (1991) of volume 30 of electrophotographic society bulletin, pp. 158-171 discloses a sensor for measuring an electrified amount in developer. However, this sensor is not a sensor for directly measuring the electrified amount in developer.
Such electrophotographic image forming apparatuses according to the related art as described above have a problem as described below. Such an electrophotographic image forming apparatus controls the electrostatic-latent-image electric-potential so as to make it constant. The apparatus subsequently attempts to stabilize the output-image density by controlling the developing-system toner-concentration under the conditions such as mentioned above. However electrified amounts in the respective color-toner particles and carrier particles may vary depending on the variation in ambience and/or aging of the apparatus. As a result, it is difficult to control a so-called printer gamma so as to make it constant, solely by means of the developing-system-toner-concentration control. The printer gamma comprises a ratio of the output-image density to the relevant input level (writing level) in the exposure process for generating the electrostatic latent image. Further, no sensor exists which can directly measure the respective electrified amounts in the toner particles and carrier particles. No means has completely been realized even for directly controlling the degree of electrification.